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Thanks Guys...Its Done Steve 04-26-2008
Posted by Steve on May 2, 2008, 2:30 pm
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>
>> So if I made a dummy valve from copper or brass to the same spec as the
>> "real" ones but left a long stem to get hold of, cut the perpendicular
>> grooves to carry the abrasive then I should be good to go?
>>
>
> As someone who cuts valve seats in race engines for a living I'm not sure
> where you're getting the above advice. The valve and seat should indeed be
> at the same angle although OE manufacturers sometimes use a very small
> (less than 1 degree) difference between them to save having to lap them in
> and let them bed into each other on their own. I don't hold with that
> approach myself. The more accurately the two faces match from the start
> the better sealing and heat rejection you get.
>
> A good choice of seat width is 4.5% of the diameter of the valve head on
> inlets and use the same seat width as the inlet on the smaller exhaust
> valves which automatically creates a slightly higher percentage width to
> aid in heat transfer. This normally equates to about 5% to 5.5% of the
> exhaust valve head size. By seat width I mean the perpendicular width not
> the horizontal.
>
> For lapping you just need a stick with a rubber sucker on the end and fine
> lapping paste. However lapping in general is bad n'kay. It actually
> creates concave surfaces on both valve and seat as the majority of the
> grinding action takes place in the centre of the contact patch. You can
> see this very clearly when you reface a heavily lapped valve on the
> grinder and the initial contact is only on the inner and outer edges of
> the seat. Any valve/seat that needs a lot of lapping hasn't been properly
> cut and really the lapping operation is mainly to check the seating and
> not to correct poor cutting.
> --
> Dave Baker
> Puma Race Engines
>

My position is all "learning by forum" not trained professional experience.
In context these valves are 3mm diameter stem and 10mm diameter across the
head.

Some of these small engine designs don't cut a seat in the head at all but
let the valve bed down on the edge of the bored chamber, others go for a
46deg seat and 45 deg for the valve. I was that concerned about getting a
good seal, I followed what was described as the "rolls royce" method - I
cut the seat at 60degrees then made a second cut at 30degrees, to end up
with seat around little more than 0.6mm wide overall perpendicular, but
with a concentric edge in the centre of the seat. So basically a
distillation of a number of contributions to forums.

Steve



Posted by TT_Man on April 27, 2008, 7:26 am
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> Finally, I've finished my attempt at building Malcolm Stride's Nemett15S.
> Never really made anything significant before, but Malcolm's article was
> that detailed I thought it was worth a shot. It fired up and ran tonight
> a bit of fiddling left to do with the carb, but it works.
>
> I didn't stretch to spark ignition but left it as a glow - motor. It's
> not exhibition standard, there are a few careless mistakes, but still
> pretty pleased with it.
>
> Here are the pics of the finished engine:
>
> www.btinternet.com/~steve.withnell/lathe/Nemett/nem2.JPG
> www.btinternet.com/~steve.withnell/lathe/Nemett/nem3.JPG
>
> The files are big <2M.
>
> So almost exactly two years to complete, I'll write down what I learned
> that wasn't in the books when I get chance.
>
> Anyway, big thanks to John, Peter(s), Dave, Tony, Keith and everyone else
> that provide help along the way and of course "Nemett" for an excellent
> constructional article.
>
> Oh and a question - anybody know where I can get a copy of the magazine
> article with Bruce Satra's valve lapping tool?
>
> Thanks Guys
>
> Steve
>
>
Very nice!
Any more details? Engine size/bhp/rpm?



Posted by Steve on April 27, 2008, 12:32 pm
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>
>> Finally, I've finished my attempt at building Malcolm Stride's
>> Nemett15S. Never really made anything significant before, but Malcolm's
>> article was that detailed I thought it was worth a shot. It fired up and
>> ran tonight a bit of fiddling left to do with the carb, but it works.
>>
>> I didn't stretch to spark ignition but left it as a glow - motor. It's
>> not exhibition standard, there are a few careless mistakes, but still
>> pretty pleased with it.
>>
>> Here are the pics of the finished engine:
>>
>> www.btinternet.com/~steve.withnell/lathe/Nemett/nem2.JPG
>> www.btinternet.com/~steve.withnell/lathe/Nemett/nem3.JPG
>>
>> The files are big <2M.
>>
>> So almost exactly two years to complete, I'll write down what I learned
>> that wasn't in the books when I get chance.
>>
>> Anyway, big thanks to John, Peter(s), Dave, Tony, Keith and everyone
>> else that provide help along the way and of course "Nemett" for an
>> excellent constructional article.
>>
>> Oh and a question - anybody know where I can get a copy of the magazine
>> article with Bruce Satra's valve lapping tool?
>>
>> Thanks Guys
>>
>> Steve
>>
>>
> Very nice!
> Any more details? Engine size/bhp/rpm?
>

It's nominally 15cc and the designer suggested in the constructional article
that it would throttle between 2000 and 8000rpm. I used to fly RC aircraft
about 20 years ago and this sounds a delight compared with those screamin
two strokes - I've only about 12mm of pipe brazed into the exhaust manifold
and it's loud but not screaming.

I think big credit is due to the designer Malcolm Stride that the article
was written with such skill as to allow me (I've no training except for
school metalwork classes about 36 years ago) to scratchbuild this. The only
parts I haven't made are the cap head screws, the bearings, the cam belt
and cam belt pulleys and the glow plug. The fuel needle in the carb was
stolen from my wife's sewing kit.

Steve


Posted by on April 27, 2008, 11:24 am
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> Finally, =A0I've finished my attempt at building Malcolm Stride's Nemett15=
S.
> Never really made anything significant before, =A0but Malcolm's article wa=
s
> that detailed I thought it was worth a shot. =A0It fired up and ran tonigh=
t a
> bit of fiddling left to do with the carb, =A0but it works.
>
> I didn't stretch to spark ignition but left it as a glow - motor. =A0It's =
not
> exhibition standard, =A0there are a few careless mistakes, =A0but still pr=
etty
> pleased with it.
>
> Here are the pics of the finished engine:
>
> www.btinternet.com/~steve.withnell/lathe/Nemett/nem2.JPGwww.btinternet.com=
/~steve.withnell/lathe/Nemett/nem3.JPG
>
> The files are big <2M.
>
> So almost exactly two years to complete, =A0I'll write down what I learned=

> that wasn't in the books when I get chance.
>
> Anyway, =A0big thanks to John, Peter(s), Dave, Tony, Keith and everyone el=
se
> that provide help along the way and of course "Nemett" for an excellent
> constructional article.
>
> Oh and a question - anybody know where I can get a copy of the magazine
> article with Bruce Satra's valve lapping tool?
>
> Thanks Guys
>
> Steve

Well done Steve a superb job that you should be very pleased with.
Looks as if it could be useful in hauling about something of a
reasonable size as well. Where was the article from? I've obviously
missed it and it looks the sort of size (larger) that I could attempt
as I could at least see most of it.

Excellent first major project Steve and it runs as well, no stopping
you now. Ashamed to report that my own first attempt at a 1.5cc diesel
only produced a couple of "putts" and very sore fingers - attacking it
with the electric starter just produced a bent conrod but I did have
the excuse that I was young and impatient at the time - just much
older now nothing else has changed. :-) Congratulations a fine and
impressive achievment, now will you make it work or is it into the
glass case for showing?

Regards

Keith


Posted by jasonballamy on April 27, 2008, 11:52 am
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looks a good job for a first project and finished just in time for the
start of his next series on the inline twin ;)

If I recall its a 15cc engine, head is about 60mm diameter to give an
idea of size and the series was in Model Engineer. I was considering it
as a second job to do while I'm making my 2" Fowler TE but will probably
go for the V twin 'Hoglet'
(http://www.pbase.com/captain_carl/image/67722872) that was in Model
engine Builder mag, bit more to see going on.

Jason


--
jasonballamy
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